The rule of 72 is used to find the number of years it takes to double your money at a given interest rate.
(72/[interest rate]) = years until a principle doubles
So, how long will it take to double your money at eight percent interest? Divide 8 into 72 and you get 9 years.
If you collect 7% on your savings in a little over 10 years the amount will be double what it is today.
The rule of 72 also means that you can determine the time
it takes for a population to double if it is growing at a steady rate by solving this function:
(72/[rate of growth]) = years for population to double
The term "the whole 9 yards" came from WWII fighter pilots in the Pacific. When arming their airplanes on the ground, the .50 caliber machine gun ammo belts measured exactly 27 feet, before being loaded into the fuselage. If the pilots fired all
their ammo at a target, it got "the whole 9 yards."
A blackjack card counter performs a simple calculation...over and over and over again. The goal is to bet more money when a deck is loaded with big cards 10,Jack, Queen,King, & Ace because the chances of a dealer busting increases. To figure out when the deck favors the player they do the following:
The card counter begins with zero. For every card that appears either they add 1, minus 1, or keep it the same.
If the card is a 2,3,4,5,6 you add 1. If the card is 10,j,q,k,ace you subtract 1. If it's a 7,8,9 the score remains the same.
So, a card counter will bet small while they keep count and if their tally reaches +5 or greater they increase their bet. This system relies on the law of large numbers which says while the bettor will lose or win money on a given day over time the bettor will have the advantage and thus be profitable long-term.
p.s. This is much easier said than done. This formula was introduced in Beat The Dealer in 1966 and the casinos are doing just fine. Good luck!
